Commonly-owned U.S. Pat. No. 7,597,502 to Allen, et al. (the “Allen Patent”), discloses use of compressible material such as ceramic or phenolic foam or cellular concrete to assist in arresting vehicles. The compressible material may, if desired, be formed into blocks or beds of particular compressive gradient strength. Fabric, film, or other wrappings may surround at least portions of the blocks, with “[a] basic function of [the wrappings being] to aid in maintaining structural integrity” of blocks “during non-emergency conditions, while being subject to tearing, breakage or other partial or complete disintegration during an arresting incident.” See Allen Patent, col. 4, 11. 43-48.
U.S. Patent Application Publication No. 2012/0057931 of Narmo (the “Narmo Application”) similarly discloses use of foamed glass aggregate for vehicle arrestments. Systems of the Narmo application include beds filled with foam glass aggregate as well as “top cover[s].” As defined in the Narmo Application, a “top cover” comprises “any cover . . . which will prevent the aggregate mass [from being] contaminated or filled with air-borne particulates, subject to plant growth, or [subject to] other environmental impacts which [interfere] with the performance of the foamed glass aggregate mass.” See Narmo Application, p. 2, col. 2, ¶ 0028.